Now I wasn't there, and I suspect OP wasn't either, but the narrative that he was sitting in his own car is disputed (as far as I know) and he may in fact have been using said car to try and ram police vehicles and officer who were operating a blockade to stop him.
Armed response are few and far between so aren't deployed lightly. If they were there it was at least under the pretext that the subject may pose a threat to life.
Again, I wasn't there and may be the cover story. But given the current climate around police shooting I would be surprised if the shot was a decision that was taken lightly.
I mean yeah, I wasn't there. I'm sure there's a lot going on with this we don't know about as well but the narrative that certainly seems most likely from the way it's been handled is that 'cock up was made'. Maybe the unnamed gunman is the fall guy. Or maybe he was trigger happy.
Either way this is being sent upstairs so far it's now being handled by the government's press office to all intents and purposes. Which to me speaks volumes.
We're working with no facts, but if they have facts that make it look less like they just shot the guy why the prosecution for murder. Not manslaughter?